This invention relates to determining the relative concentrations of fluids within subterranean reservoirs by measuring the chromatographic separation of tracers having distinctly different partitioning coefficients with mobile and immobile phases (such as water and oil phases) of fluids within the reservoirs. More particularly, the present invention relates to improving a process for making such determinations by injecting an aqueous solution of reactants which form tracers inclusive of one which is significantly partitioned between such mobile and immobile phases and one which is substantially completely dissolved in the mobile phase.
In 1969 a method for determining the relative amounts of mobile and immobile fluid phases within a subterranean reservoir by injecting carrier fluid containing a reactant capable of forming within the formation at least two tracers which have different partitioning coefficients between the carrier fluid and the immobile fluid phase (exemplified by the tracers formed by a hydrolyzable organic ester) and measuring the separation of the tracers, was described in U.S. Pat. No. 3,623,842. U.S. Pat. No. 3,751,226 by R. J. Hesse and R. F. Farmer relates to improving such a process by injecting a solution in which the tracer forming reactant is a hydrolyzable beta-keto ester such as ethylacetoacetate. U.S. Pat. No. 3,847,548 relates to improving such a process by injecting carrier fluid containing tracers which partition differently in respect to temperature changes and injecting that fluid at a temperature different from the reservoir temperature. U.S. Pat. No. 3,856,468 relates to improving such a process by injecting carrier fluid containing both a precursor which forms a tracer material that partitions between the fluid phases and a tracer material which is inert and substantially completely dissolved in a mobile phase. U.S. Pat. No. 3,990,298 relates to improving such a process by injecting a carrier fluid containing a plurality of precursors each of which forms a tracer which has a distinctive partition coefficient with at least one immobile fluid phase within the reservoir. U.S. Pat. Nos. 4,099,565 and 4,168,746 relate to uses of such a fluid saturation determining process in the course of evaluating the effectiveness of a design process for recovering oil.